Metal-hardening process



- ofw Patented May 20,1930

UNITED STATES.

PATENT orrlclz GEORGE A. FLECKENSTEIN, OI STRATFORD, EDWARD Ml. HANF, OF BRIDGEPORT, AND MAX L. WATEBMAN, OF FAIREIELD, CONNECTICUT, ASSIGNORS TO THE SINGER MANUFACTURING COMPANY, OF ELIZABETH,.NEW JERSEY, A CO NEW JERSEY Ho Drawing.

This invention relates to improvements in the process of case-hardening articles andhas for its object to provide an eflicient method of case-hardeningportions only of articles and save a ver substantial art of the time and amount 0 labor hereto ore required in case-hardening portions of articles.

For certain classes of work it is desirable, whencase-hardening articles, to leave a portion or difi'erent portions of the articles relativel soft. In order to manufacture articles fiich portions only are case-hardened and the remaining portions are relatively soft, various expedients have been heretofore proposed to prevent penetration at the desired soft portion of the article by the hardening ingredient derived from the compound or bath employed in case-hardenin Probably the ex edient most widely use heretofore, comprised copper plating the article portions to remain relatively soft, preparatory to case hardening, and removing the copper-plating after the case hardening operation.

This prior method was not only cumbersome, but in. order to render the desired portions of the article efliciently impervious to the hardening material, it was necessary to copper plate said portions of the article to a thickness of approximately .003 of an inch or more, involving a plating period of from minutes to an hour. Furthermore, in a large number of instances, dependent of course upon the function of the article, the increased size of the article due to the copper plating 4 necessitated removal of the copper plating after the hardening was completed. This involved a still further waste in time and labor.

According to the present invention, a relatively thin coating of chromium is plated upon the article at the portion of the article to be rendered impervious to the hardening element of any of" the usual case-hardening operations. It has been determined by ex-. periment that chromium platlng 1s so impervious to the hardening element that the chromium coating is highly eflicient even with a film f.thickness of between .00005 and .00006 of an inch. It will be appreciated that 7 this slight increase in thickness of the article is negligible for all ordinary purposesfland METAL-HABDENING PROCESS Application filed November 23, 1928. Serial No. 321,507.

therefore the present process 'obviates re- .moval of the coating subsequently to casehardening.

RPORATION 01!,

Not only is it unnecessary to subsequently v remove the coating of chromium, but the apphcation of the coating of chromium involves only a small fraction of the time consumed in applying thenecessa'ry coating of,

for instance, copper. It has been found by experlment that with a chromium plating solution temperature of from 100 to 113 Fahrenheit and a current density of about 150 amperes per square foot, a thoroughly efiicient coating or film of chromium of approximately .00006 of an inch in thickness is applied to the article in from five to ten minutes, the average chromium plating time bemg about 8 minutes, instead of approximately the hour of plating time required in the same operation with, for instance, copper.

However, 1f it is desired for any reason to remove the chromium, lating this may be effected. in a fracton o the short time requlred for the plating and without pitting or scarring the article, as frequently occurs upon removal of the copper-plating.

The chromium plating may be effected electrollytically in any well known manner by app ying to portions of the article to be later case-hardened any suitable lacquer or similar material which repels chromium plating, before the article is placed in the plating bath. After the article has been plated at the desired portions thereof with the relatively thin coating of chromium, the article is removed from the plating bath and the chromium-repelling lacquer is suitably removed. The article is then ready for casehardening in any usual .manner, as for instance, by carburlzation with anyof the ordinary compounds or; by the cyanide process, I

the chromium plating being effective in any of the usualmethods of case-hardening.

Thethin coating of chromium being eifi- 9 ciently impervious to the hardening element it is apparent that the chromium-plated portion or portions of the article will be left relatively soft upon the completion of the casehardening operation. i

Having thus set forth the nature of the invention, what we claim herein is:

1. The process of case-hardening a portion only of an article, comprisin plating the portion of the article to be 1e t unhardened .with a thin coating of chromium whereby the plated portion is not materially increased in size,' and then subjecting both plated and unplated portions of the article to the hardening operation, whereby to case-harden the unplated portion of the article.

2. In the process of case-hardening, that I step comprising subjecting to the hardening operation an article of which a portion thereof is plated with chromium to a thickness ofapproximately .00006 of an inch, whereby the unpla-ted portion remaining of the article is hardened. I

In testimony whereof, we have signed our 0 names to this'specification.

GEORGE A. FLEOKENSTEIN. EDWARD M. HANF. MAX L. WATERMAN. 

